The principle of increasing the turbulence of mixed media during chemical reactions is commonly achieved in chemical conversion reactors by the use of nozzles, stirrers, etc.; however, when extra energy needs to be added to the process chemicals it has been proven useful to increase the energy density accordingly--at the point of highest relative motion of the molecules in respect to each other.
During experiments with energy deposition from electrical currents in liquids and gases, it has been shown that the reactor efficiency, Reff, (that is the conversion of chemical compounds passing through the reactor at a single pass) increases when higher energy concentration accompanies higher turbulence.
The reactor efficiency (as defined above) is expressed as the product of: a form factor K (which depends on the reactor geometry and other design parameters), the energy input per useful volume of the reactor (Wdv) and the reaction time (Trv) of the process media in the reactor. This efficiency increases when the same energy input is used at higher energy concentration and correspondingly shorter retention time but at higher dynamic turbulence.
This effect was first observed in reactors that had high energy concentration near electrical electrodes at the point where the electrodes reach into the reactor vessels and when the diameter of the reactor vessels was changed to provide faster or slower fluid flow speeds and correspondingly shorter or longer retention times.
It is believed that this effect is due to the average recombinant time constant of the reactor products that were initially split during the application of electrical currents through the chemical process media.
When the turbulence is high and the reaction products are in their reaction phase, the likelihood of suitable molecules finding their respective counterparts is also high. However, unless there is enough energy available for the desired reaction to work in the saturation region of the reactor all the time (which may not be energy efficient), a certain percentage of the previously excited molecules decay rapidly when no energy is present and these do not undergo reactions, therefore making the reactor efficiency less than 100%.
In random-heat-reactors this effect can be observed by applying different pressures to the process media in the reactor vessel and observing the chemical effects due to the corresponding change in the inter-molecular spacing.
However, even though random-heat-reactors are commonly used (since they are generally fairly easy to construct), random-heat-reactors tend to be inherently somewhat inefficient chemical conversion devices because seldom do their reaction products leave the reactor at the desired end-use temperature, e.g., room temperature, after the process. (Sometimes the overall energy efficiency of the conversion reactor can be improved by using heat recovery methods.)
Better energy use and efficiency can be accomplished in, for example, shock wave driven reactors, ultrasonic or photon activated reactors, or reactors that use radiation or pressures from electrically or mechanically initiated plasmas via shockwaves or high flow speed conditions.
Recent experiments in ethylene conversion using the shock wave generated by a high speed nozzle is one example.
Another example of the dependence of the chemical reactor conversion efficiency on the retention time and mixing conditions (turbulence) is the processing of hydrocarbons (HC) dissolved in water with HO radicals made from hydrogen peroxide under the influence of UV light.
There, with decreasing concentrations of HC the retention times in these reactors have to be increased successively in order to achieve higher and higher purity of the processed water. This is done by splitting the flow into parallel reactors or using reactor vessels with successively larger process media processing volumes connected in series or parallel.
One of the most energy efficient reactors is the ultrasonic or electrohydraulic (EH) type, if overall energy input to chemical product output is used to define energy efficiency. These devices incorporate high turbulence and high energy densities throughout the active reactor-volume.
However, the heat losses in the electrode regions in the electrohydraulic systems and the transducer losses in the ultrasonic type of conversion reactors as well as the losses in the power conversion systems still are detrimental to large system applications.
Plasma reactors can avoid the complexities in the electrical power switching and power systems but the operation of plasma arcs in chemical processing is limited. Depending on the process, the entire process media throughput-volume has to be raised to temperatures which can be as high as the plasma temperature and then cooled down again, which often results in very poor energy management.